Fullerenic structures and such structures tethered to carbon materials

ABSTRACT

The fullerenic structures include fullerenes having molecular weights less than that of C 60  with the exception of C 36  and fullerenes having molecular weights greater than C 60 . Examples include fullerenes C 50 , C 58 , C 130 , and C 176 . Fullerenic structure chemically bonded to a carbon surface is also disclosed along with a method for tethering fullerenes to a carbon material. The method includes adding functionalized fullerene to a liquid suspension containing carbon material, drying the suspension to produce a powder, and heat treating the powder.

PRIORITY CLAIM

The present divisional application claims priority to U.S. patentapplication Ser. No. 10/675,140 filed on Sep. 30, 2003, which isincorporated herein by reference.

GOVERNMENT FUNDING

The government has certain rights in this invention pursuant to Dept. ofEnergy Grant No. DE-FG02-85ER45179 and Grant No. DE-FG-0284ER13282.

BACKGROUND OF THE INVENTION

The present invention relates to fullerenic structures and suchstructures tethered to carbon materials.

Fullerenic structures are carbon compounds that include closed-cagedcompounds such as fullerenes and nanotubes. One of the first fullerenesdiscovered was the version containing 60 carbon atoms (C₆₀) made up ofadjacent carbon pentagon and hexagon rings. Other fullerenes such asC₃₆, C₇₀, and C₉₀ have been observed and analyzed. It has beenspeculated that fullerenic structures both smaller than and larger thanC₆₀ exist in, for example, combustion-generated soot.

Because fullerenic structures are small (C₆₀ has a diameter ofapproximately 7 Å) and typically occur in very low concentrations insoot, their presence is difficult to detect. Furthermore, fullerenes aredifficult to detect and characterize because they are often verystrongly bound to, or within, the material with which they are condensedin the synthesis process thereby preventing easy removal for chemicalanalysis. Examples are fullerenes smaller than C₆₀ all of whichnecessarily contain adjacent pentagons in their structure and arestrongly curved and strained and hence more interactive leading tostrong bonding. Similarly, fullerenes larger than may also be stronglybonded to other structures because the size of larger fullerenesfacilitates extensive contact thereby increasing the opportunity forbonding interactions.

It has been suggested that fullerenes bound to carbon black pigmentwould be useful for making an improved ink for use in, for example, aninkjet printer. See, Japanese Laid Open Publication no. 11-140342,published May 25, 1999. This reference, however, does not establish thechemical bonding of fullerenes to carbon black.

SUMMARY OF THE INVENTION

In one aspect, the invention comprises fullerenes having a molecularweight less than that of C₆₀ with the exception of C₃₆. In anotheraspect, the invention comprises fullerenes C₅₀, C₅₈, C₁₃₀, and C₁₇₆. Inanother aspect, the invention is the above-mentioned fullerenes in anisolated state. In yet another aspect, the invention is a single-walledcarbon nanotube having a diameter less than that of C₆₀ and notassociated with a three-dimensional support matrix. In yet anotheraspect, the invention is a fullerenic structure including a fullerenechemically bonded to a carbonaceous material.

In still another aspect, the invention is a method for tetheringfullerenes to a carbon material including the steps of addingfunctionalized fullerene to a liquid suspension containing a carbonmaterial. The suspension is dried to produce a powder and the powder isheat treated to produce the fullerene chemically bound to the carbonmaterial. In one embodiment of this aspect of the invention, thefunctionalized fullerene is dichloromethano [60] fullerene. This methodmay include the additional step of sealing the dried powder in a tubefilled with an inert gas followed by heat treatment of the tube in afurnace.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an HRTEM image of a particle from a pure carbon black sample.

FIG. 2 is an HRTEM image of a particle from a post-extraction tetheredfullerene sample.

FIG. 3 is a cartoon illustrating the measurement method used forstructure diameter size distribution determination.

FIG. 4 is an HRTEM image of flame soot with gold island deposits andshowing structures smaller than C₆₀.

FIG. 5 is an HRTEM image of flame soot showing structures both largerand smaller than C₆₀.

FIG. 6 is an HRTEM image of flame soot showing structures larger than,smaller than, and the size of, C₆₀.

FIG. 7 is a size distribution histogram of structures measured in HRTEMimages of flame-generated soot.

FIG. 8 is an HRTEM image of a pure C₆₀ sample.

DESCRIPTION OF THE PREFERRED EMBODIMENT

As discussed above, detection of fullerenes is difficult because theirconcentration is low and they are often tightly bound to the materialwith which they were condensed in the synthesis process making removalfor chemical analysis difficult. The composition of matter inventionsdisclosed herein have been observed using high resolution transmissionelectron microscopy (HRTEM). This technique provides a means forextending the detection and analysis of fullerenes to lower limits ofdetection than can be attained by conventional chemical analysis. Forexample, circular objects approximately the size of C₆₀ and C₇₀fullerenes can be seen in HRTEM images of soot not only from certainlow-pressure benzene/oxygen flames well known to contain fullerenes butalso from atmospheric-pressure ethylene/air flames in which fullerenescould not be detected by state of the art chemical analysis. Grieco W J,Howard J B, Rainey L C, Vander Sande J B. Carbon 2000; 38:597. Thecontents of this reference and all of the references cited below areincorporated herein by reference.

Example 1

Three different samples were prepared for investigation by HRTEM. Thefirst sample was pure carbon black (Regal 330; Cabot Corp.) suspended ina toluene solution. The other two samples were prepared from a portionof the carbon black-toluene solution to which was added a specifiedamount of dichloromethano[60]fullerene. In this functionalizedfullerene, the carbon atom of the functional group is bridged to twocarbon atoms of the fullerene molecule. After a uniform dispersion wasensured with vigorous mixing, the toluene was allowed to evaporate andthe resulting dry powder mixture was sealed inside an argon-filled glasstube. The entire unit was then heat treated at approximately 400° C. for4.5 hours in a tubular furnace (Lindberg Model 55036) and then cooled.The material was removed from the tube and divided into two parts. Oneof these two samples was not treated further and hence consisted ofcarbon black with tethered fullerenes and any fullerenes that remaineduntethered. This sample is referred to as pre-extraction. The other ofthese two samples was extracted by sonication in toluene for 13 minutesfollowed by vacuum filtration with a 0.45-μm nylon filter to remove anyuntethered fullerenes. Thus, this sample, referred to aspost-extraction, consisted of carbon black with only tetheredfullerenes.

A diluted suspension of each of the three samples in toluene wasdeposited onto a lacey carbon grid and the toluene was allowed toevaporate. The samples were analyzed in a JEOL 2010 electron microscopeoperating at 200 kV. The images obtained were analyzed for the presenceof fullerene-type structures, i.e., structures that appear to becompletely closed cages. In each image, the number of fullerene-typestructures per length of perimeter, referred to as linear concentration,was determined and the diameter of each of those structures wasmeasured. The data then were aggregated across all the images of aparticular sample to provide fullerene linear concentration data andfullerene size distribution data.

FIGS. 1 and 2 show two images that are representative of the imagesanalyzed from the different carbon black samples. FIG. 1 is an image ofa particle taken from pure carbon black while FIG. 2 shows a particlefrom the post-extraction sample.

The black dashes in FIG. 2 are observer-added indications of structuresthat were deemed to be fullerenic and included in the concentration andsize data. The absence of black dashes in FIG. 1 highlights the lack offullerene-type structures in the carbon black sample. Only carbonstructures along the periphery of the particles were analyzed as onlythe periphery was thin enough to allow for observation and accuratemeasurements of the structures. Hebgen P, Goel A, Howard J B, Rainey LC, Vander Sande J B. Proc Combust Inst 2000; 28:1397. The hand-drawnblack line in the inset to FIG. 2 shows the boundary between the areathat was analyzed and the particle interior, whose thickness presentstoo many stacked carbon layers to allow for accurate structuralidentification. It is unclear whether perceived structures in theparticle interior inside the boundary are in fact single structures orthe result of superpositioning of two or more different structures. Onlythe material outside the boundary was sufficiently thin to ensureinterpretable observations. Qualitatively, the images show quite clearlythat the carbon black doped with tethered fullerenes has many morefullerene-type structures than the pure carbon black particles.

Quantitative analyses of the same images reinforces the qualitativeobservation. FIG. 3 shows the method used to perform the quantitativeanalyses. It can be seen from this cartoon, corresponding to the fivecondensed structures in the inset to FIG. 2, that both vertical andhorizontal height (diameter) were measured and then averaged. Thisaveraged diameter was then used for size distribution purposes. Table 1gives a summary of the fullerene concentration data.

TABLE 1 Fullerenic Structures No. of Perimeter per 1000 FullerenicLength nm of Sample Number and Description Structures (nm) perimeter 1.Without tethered C₆₀ 21 1775 12 2. With tethered C₆₀; pre-extraction 2092220 94 3. With tethered C₆₀; post-extraction 172 1970 87

From Table 1, it is seen that both samples containing tetheredfullerenes have a fullerene concentration almost an order of magnitudegreater than the concentration of what appears to be fullerenes in thepure carbon black sample. It should be noted that the post-extractionsample does have a slightly lower concentration than the pre-extractionsamples. This is not surprising as it is expected that less than 100% ofthe functionalized fullerenes would react with the carbon black, leavingsome untethered fullerenes to be separated during extraction.

It should be noted also that both the pre- and post-extraction samplesexhibit concentrations less than what would correspond to the totalamount of functionalized fullerenes added in the experiment. Consideringthe relative amounts of carbon black and functionalized fullerenesutilized, and assuming a uniform distribution of fullerenes over thesuperficial surface of the carbon black, the calculated areaconcentration of fullerene molecules would be 0.25 molecules/nm². Thecorresponding linear concentration of fullerenes would be 0.50molecules/nm. Both tethered samples yield a linear concentrationapproximately 20% of this theoretical value indicating that many of thefullerenes are not observed. This result is not surprising given thedifficulty of finding and observing fullerenes on the carbon blackparticles.

In an experimental situation similar to that disclosed herein, Cox etal. deposited C₆₀ on MgO crystals supported on holey carbon films. Cox DM, Behal S, Disko M, Gorun S M, Greaney M, Hsu C S, Kollin E B, MillarJ, Robbins J, Robbins W, Sherwood R D, Tindall P. J Am Chem Soc 1991;113:2940. Circular contrast patterns with about 0.8 nm diameter,consistent with that of C₆₀, were observed on the MgO crystals and couldbe seen most clearly on the edges of crystals hanging over holes in thesupport film. The circular images were not seen on MgO crystals withoutC₆₀ deposition. The Cox et al. work and the data presented aboveestablish that the contrast observed, for instance in FIG. 2, isconsistent with single C₆₀ molecules. It should be noted that thecontrast in FIG. 2 is exactly analogous to that in FIG. 8, which isknown to show C₆₀ molecules. The order of magnitude increase in observedfullerenic-type structures in doped-with-C₆₀ samples strengthens theconclusion that C₆₀ molecules are being observed. This coupled with thequalitative observations indicates quite strongly that fullerenes havebeen tethered to the carbon black surface, and furthermore, that thesefullerenes are observable with HRTEM.

Nonetheless, precautions must be taken to reduce the influence ofradiation damage and/or beam heating on the observations. Suchinfluences include degradation of the sample, incorporation of smallerstructures into larger ones, and migration of molecules. All three ofthese scenarios have been observed during HRTEM imaging and all cancontribute to an artificially low frequency of fullerene observations.For example, we have observed C₆₀, and other fullerenic molecules,migrating “behind” the carbon black under some observation conditions,in accord with earlier reports. Fuller T, Banhart F. Chem Phys Lett1996; 254:372.

Precautions must be taken to analyze images of a particular soot area atall possible focal lengths. The position of the soot particles along theoptic axis of the instrument will create variations in contrast andimage characteristics which can render some structures uninterpretable.This effect can compound errors due to other influences discussed aboveand, again, can suppress successful observation of fullerenicstructures. Thorough focal series can help to alleviate this source oferror.

While care is taken to minimize the effects of these imaging artifacts,some error will still be incorporated into the imaging results. Thisreduction in fullerenic structure observations gives a plausibleexplanation as to why, as mentioned above, the observations account foronly 20% of the expected theoretical value. Normally, a 20% agreementwould be cause for concern but given the fact that we observe still anorder-of-magnitude increase in fullerenic structures with tetheredfullerenes, our conclusions are not weakened.

The method disclosed herein tethers fullerene molecules by chemicalbonding to a carbon surface. Those skilled in the art will appreciatethat the method disclosed herein can be used to tether fullerenes to thesame or other fullerenes or fullerene derivatives including endohedralfullerenes and metallized fullerenes, fullerenic nanostructuresincluding single-walled and multi-walled carbon nanotubes, nested oronion structures or spherical, ellipsoidal, trigonous or other shapes,single- and multi-layered open cage structures of various radii ofcurvature, fullerenic soot and fullerenic black; and any form ofgraphitic carbon; any form of diamond; and any form of diamond-likecarbon; and any form of amorphous carbon.

Those skilled in the art will further appreciate that the methoddisclosed herein is applicable to the situation in which the fullerenebeing tethered is a fullerene derivative or functionalized fullerenecontaining a functional group chosen so as to give the functionalizedfullerene, and in turn the surface or material to which it is tethered,desired properties such as: acidic, basic, hydrophobic, hydrophilic,oxidizing, reducing, radical, metallic, electrical, magnetic, or otherstructural, chemical, biological or physical properties. It will also beappreciated that the tethers may differ in length, stiffness, electricalconductivity or other properties. For example, tethers of differentlengths may be achieved by the use of chemical chains, such as aliphatichydrocarbon chains of different lengths and tethers of differentstiffness may be achieved by the use of chemical structures such asalkane, alkene, alkyne, fused or cross-linked aromatic structures, etc.

Example 2

Additional HRTEM analyses were performed on soot material collected froma premixed benzene/oxygen/argon flame that has been extensivelycharacterized and studied previously. Grieco W J, Howard J B, Rainey LC, Vander Sande J B. Carbon 2000; 38:597; Grieco W J, Lafleur A L,Swallow K C, Richter H, Taghizadeh, K, Howard J B. Proc. Comb. Inst.1998; 27:1669-1675. The conditions of this flame are: pressure, 40 Torr;gas velocity at burner, 25 cm/s (25° C.); fuel equivalence ratio, 2.4(atomic C/O ratio, 0.96); and percentage diluent in feed gas, 10% argon.Samples of soot and all other condensables from this flame werecollected in the manner described previously (Grieco W J, Howard J B,Rainey L C, VanderSande J B. Carbon 2000; 38:597) and HRTEM analysis wasdone using the same JEOL 2010 operating at 200 kV as in Example 1. Goldislands were deposited on the surface of several of these samples toprovide a magnification calibration for the HRTEM images. Gold has astable planar structure with a constant interplanar spacing of 2.039 Åfor the {111} atomic planes. By observing and measuring this knownspacing in an image, the image length scale thus is calibrated allowingthe dimensions of other structures to be accurately measured. Thiscalibration was used to measure the sizes of several of the closed-cagestructures that were observed in the images and the data were compiledacross all of the samples into a size distribution histogram.

The accuracy of the electron microscope as determined by the abovecalibration was ±0.01 nm. The accuracy of the measurement of thediameter of a fullerene molecule is limited by the observer's ability toidentify the true edge of the hollow circular HRTEM image of themolecule. The observer was able to specify the diameter of the image ofa fullerene molecule with a precision of ±0.01 nm or better.

FIGS. 4 through 6 show representative images taken from the analysis ofsamples of flame-generated soot. The striped patterns on FIG. 4 are thelattice fringe images of the {111} planes from the deposits of gold thatwere used to calibrate the microscope. FIGS. 5 and 6 show other areas ofthe soot and several key structures are indicated by the arrows. Thenumbers associated with the highlighted structures are the observeddiameters using the gold calibration as identified in FIG. 4. It can beseen from the indicated structures in FIGS. 4 through 6 that not onlyare structures the size of C₆₀ and larger observed (structures marked6.85 Å, 8.6 Å, and 10.3 Å), but those smaller than C₆₀ are prevalent aswell (structures marked 5.2 Å).

The size-distribution histogram obtained from the measurement of thesestructures is seen in FIG. 7. The size is an average of the major andminor axes of these, generally non-round structures. In the histogram,the numbers along the x-axis represent the bins that were used toseparate out the measurements. The arbitrary nature of the bin sizes andcut-offs is a consequence of the resolution limit of the measurementtechnique. It can be seen from FIG. 7 that there is a significant peakin the bin containing 7 Å, which is the diameter of C₆₀. In addition,FIG. 7 shows that structures of average dimension both larger andsmaller than C₆₀ are prevalent in the samples. This indicates that weare in fact observing and identifying structures that are not onlylarger than C₆₀ but smaller as well.

The gold island calibration method was developed and used to analyzeimages of flame-generated soot. The high precision and accuracy of thismethod give it a significant advantage over both the measurement methodfrom Hebgen, et al. (Hebgen, P, Goel A, Howard J B, Rainey L C,VanderSande J B. Proc Combust Inst 2000; 28:1397) and the method used inthe tethered fullerene Experiment 1 above. The observation of structuressmaller than C₆₀ in the experiments using gold calibration (FIGS. 4through 7) proves conclusively that such small structures do exist andthat they are not artifacts of the method. The measured diameters rangefrom about 0.5 nm to about 1.2 nm (see FIG. 7). A simple calculationusing 0.7 nm as the diameter of C₆₀ and approximating all fullerenemolecules as spherical shells whose mass is proportional to the squareof the diameter gives 0.5 nm as the diameter of C₃₆ and 1.2 nm as thediameter of C₁₇₆. The diameter of C₃₆ as represented by the carboncenter to carbon center distance has been reported to be 0.5 nm. (CoteM, Grossman J C, Louie S G, Cohen M L. Bull Am Phys Soc 1997; 42:270;Grossman J C, Cote M, Louie S G; Cohen M L. Bull Am Phys Soc 1997;42:1576; and Grossman J C, Cote M, Louie S G, Cohen M L. Chem Phys Lett1998; 284:344. Average diameters of selected structures marked forillustration in FIGS. 4-6 include 0.52 nm, 0.685 nm, 0.86 nm, and 1.03nm, corresponding to C₃₆, C₅₈, C₉₀, and C₁₃₀.

Many other closed-cage structures with sizes corresponding to C₅₀ andother fullerenes, and fullerene-like structures larger than the C₁₇₆mentioned above, were also observed. A striking feature of theobservations was a preponderance of fullerenes that have not beenobserved in conventional chemical analyses, presumably because they arehighly reactive and hence unstable and difficult to synthesize inobservable quantities, or strongly attracted to soot or other carbonmaterial with which they are formed and from which they are difficult toremove for chemical analysis. This observation provides grounds forexpecting that other unstable species, such as C₂₀ and single-walledcarbon nanotubes having diameters less than C₆₀ and not in athree-dimensional support matrix, could be stabilized on a carbonsupport and observed with the methods of this study. Fullerene C₂₀ hasonly been observed spectroscopically and for only fractions of amillisecond. Single-walled carbon nanotubes with diameters less than C₆₀have only been observed within porous materials such as zeolites whichprovide a support structure within which the tubes are grown.

The confirmed existence of sub-C₆₀ fullerenes also indicates thepresence of adjacent carbon pentagon rings in these fullerenes, whichhas important implications for bulk soot properties. Adjacent pentagonsresult in unique structural and electrical properties in the soot thatcan be exploited for the development of commercially useful products.

Example 3

The fullerenes observed in Example 2 are separated and isolated from thematerial with which they are condensed in the synthesis process. Forfullerenes smaller than C₆₀ the fractionation and analysis methods ofPiskoti et al. is used. Piskoti C, Yarger J, Zettl A. Nature 1998;393:771. Fullerenes larger than C₆₀ are isolated by solvent extractionand high pressure liquid chromatography analysis. See, Richter H,Labrocca A J, Grieco W J, Taghizadeh K, Lafleur A L, Howard J B. J PhysChem B 1997; 101:1556.

Example 4

A sample of C₆₀ molecules (99.5% pure; SES Corporation) was examinedunder HRTEM. The fullerenes were dissolved into toluene and drops of thesolution were placed on TEM grids. The toluene was allowed to evaporatebefore the HRTEM analysis.

FIG. 8 shows a representative HRTEM image from the analysis of C₆₀precipitated from solution directly onto the TEM grid. The C₆₀ moleculeshave taken a crystalline form with a two-fold symmetry that is visible.Comparing the length scale to the black centers of the individualmolecules reveals a diameter of about 0.7 nm as expected for C₆₀molecules. The measured center-to-center distance between the moleculesis 1.01 nm along two of the crystallographic directions and 1.14 nmalong the third direction.

As stated earlier, the contents of all of the references cited in thisspecification are incorporated herein by reference.

It is recognized that modifications and variations of the invention asdisclosed herein will be apparent to those skilled in the art, and it isintended that all such modifications and variations be included withinthe scope of the appended claims.

1. A method for tethering a fullerene to a carbon material comprising:adding functionalized fullerene to a liquid suspension containing carbonmaterial; drying the suspension to produce a powder; and heat treatingthe powder.
 2. The method of claim 1 wherein the functionalizedfullerene is dichloromethano [60] fullerene.
 3. The method of claim 1wherein the functionalized fullerene is dibromomethano [60] fullerene.4. The method of claim 1 further including sealing the powder in a tubefilled with an inert gas.
 5. The method of claim 4 wherein the tube isheat treated in a furnace.
 6. The method of claim 5 wherein the tube isheat treated at approximately 400° C. for 4.5 hours.
 7. The method ofclaim 1 wherein the carbon material is a fullerene.
 8. The method ofclaim 1 wherein the carbon material is a fullerene derivative.
 9. Themethod of claim 8 wherein the fullerene derivative includes anendohedral fullerene.
 10. The method of claim 8 wherein the fullerenederivative includes a metallized fullerene.
 11. The method of claim 1wherein the carbon material is a fullerenic nanostructure includingsingle-walled and multi-walled carbon nanotubes.
 12. The method of claim1 wherein the carbon material is a nested or onion structure.
 13. Themethod of claim 1 wherein the carbon material is spheroidal,ellipsoidal, trigonous-shaped fullerenic structures.
 14. The method ofclaim 1 wherein the carbon material comprises single and multi-layeredopen cage structures having a range of radii of curvature.
 15. Themethod of claim 1 wherein the carbon material is fullerenic soot. 16.The method of claim 1 wherein the carbon material is fullerenic black.17. The method of claim 1 wherein the carbon material is graphiticcarbon.
 18. The method of claim 1 wherein the carbon material isdiamond.
 19. The method of claim 1 wherein the carbon material isdiamond-like carbon.
 20. The method of claim 1 wherein the carbonmaterial is amorphous carbon.
 21. The method of claim 1 wherein thefunctionalized fullerene contains a functional group selected to givethe functionalized fullerene and a surface of the material to which itis tethered a desired property.
 22. The method of claim 21 wherein thedesired property is selected from the group consisting of acidic, basic,hydrophilic, hydrophobic, oxidizing, reducing, radical, metallic,electrical, magnetic, structural, chemical, biological, or physicalproperties.
 23. The method of claim 1 further including use of chemicalchains selected to achieve a desired tethered length.
 24. The method ofclaim 1 further including use of chemical structures selected to achievea desired tether stiffness.
 25. The method of claim 24 wherein thechemical structures comprise alkane, alkene, alkyne, fused orcross-linked aromatic.
 26. The method of claim 1 further includingchemical structures selected to achieve a desired electricalconductivity.